Inorganic Nitrogen Addition Affects Soil Respiration and Belowground Organic Carbon Fraction for a Pinus tabuliformis Forest
Round 1
Reviewer 1 Report
The manuscript is valuable as it confirms that N deposition can impact soil respiration. I believe the paper could be published in Forests with extensive improvement in English language usage, and if my concerns highlighted below are addressed.
Extensive English language editing is needed, i.e., superfluous use of “the” in some sentences, but lacking the use of “the” in others. For example:
Introduction
Line 37: “the nitrogen deposition”, and “the anthropogenic activities”, then on line 38 “During last…” instead of “during the last”.
Line 39: per above, “and been predicted” should be “and has been predicted”
The manuscript will be greatly improved by a native English speaker’s line edits
-some mention of what the sources of atmospheric N deposition are will be helpful in the introduction
-line 70: “the global change model”? please define
-why is Pinus tabulaeformis a model system? For an international audience it must be defined why this species is of importance
Materials and Methods
Line 88: Pinus tabuliformis is different than the title and introduction, a quick Google search revealed that Pinus tabuliformis (Manchurian red pine) is the correct nomenclature. Also, Latinate names must be italicized
Line 94: again, consistency in plant names!!!
Line 98: how was the N addition “evenly sprayed”? more detail needed
Line 131: “regularly collected” specifically how often was this? Maybe a table with sample dates for each collection would be helpful? Could go in supplemental information
Line 145: extraneous “m” between chloroform and fumigation
Lines 151-152: weird use of “averagely”; see above about need for editing for an English language readership
Line 161: citation for R needed
Results
Line 167: summer soil respiration “took over”? I don’t understand this. Based on the next sentence, I’m given to think this means the annual proportion of Rs? Very unclear
Line 172: stick with the designations, i.e., N20 instead of again giving the amount added (this was already specified in the methods)
Fig. 1: these are not “gradients” but different N additions. Overall you have created a gradient of N addition, but each individual treatment (N20, N40, etc) does NOT make an individual gradient.
Table 2: Did you test for homogeneity of variance? If so this must be mentioned in section 2.5. You cannot justify ANOVA without proper pre-model testing.
Fig. 3: The relationship in b) seems to be better fit with an exponential model and d) seems to be a quadratic relationship. Did the authors consider non-linear models to fit the data? I suggest re-analyzing with non-linearity in mind, and think about what that might mean for how litter inputs and dissolved organic C control soil respiration. Obviously you do consider this in Figure 4.
Discussion
Line 295 on: without a better description of these soils (clay fraction, pH), or some Al/Mg data this is a stretch. I think this could be a reasonable explaination (biogeochemically speaking…) but I’d like to see a table with the latent soil properties beyond just the FAO taxonomic designation giving in section 2.1.
Author Response
Dear reviewer:
Many thanks to you for reviewing our manuscript. Your constructive suggestions have greatly increased the paper quality in article organization and result analysis. The errors were corrected strictly according to your comments, and the details about how to change them are listed in the file attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Zhang et al. investigate the effect of Nitrogen addition on annual and seasonal soil respiration, microbial biomass, soil dissolved organic carbon and fine root biomass. They find that annual soil respiration and fine root biomass was decreased by nitrogen addition, but that proportions of autumn and winter respiration were increased. Soil respiration was correlated to fine root biomass, microbial biomass content and soil dissolved organic carbon. From this, they conclude that nitrogen addition influenced soil organic transformation and soil respiration due to depressing fine root production
The authors have set up an intensive experiment and received interesting results. However, I find the manuscript very difficult to read due to language issues. Not being a native speaker myself, I feel that the manuscript would strongly benefit from an English language editing. It was hard for me to understand some of the sentences. Furthermore, a lot of spelling mistakes make the reading unpleasant.
General comments:
The text is difficult to follow with all the abbreviations. A list of all abbreviations would help.
Methods: it would be very helpful to have a figure showing the study design. For me the study design is not clear based on the description in lines 99-102.
Discussion: The results should be discussed in the light to other references and also in context to results that were found in other N addition experiments. I feel that the discussion is missing a central theme and that it is not well organized.
Conclusions: The conclusions are just a repetition of the results.
Specific comments:
Title: The title is quite long.
L14: ecosystems
L16: under the future scenarios of global change
L25: An increase of the seasonal proportion of ca 1-2% seems not very large. Maybe it would be helpful to put these numbers in context to the absolute numbers.
L28-29: repetition to line 22
L 88: Is this a representative forest type for China? Species names should be written in italics.
L96: do you mean 1880 trees ha-1
L99: it would be interesting to relate N addition levels to expected increase of N input in China
L121, eq.2: How is this equation derived? Why do you use 3600*12?
L165: in average
L172: at which N addition level?
Fig.1: axis label in Fig 1b should be Proportion
Table 1: Explain abbreviation in the Table footnote. What is Ri, not explained in text.
Table 2: Which R was tested? Ri or Rsi or R10, etc?
Fig.2: I am wondering that N40 treatment is not significantly different from other treatments in a), b) and c)
L227: I do not understand the sentence
Author Response
Dear reviewer
Many thanks to you for reviewing our manuscript. Your constructive suggestions have greatly increased the paper quality in article organization and result analysis. The errors were corrected strictly according to your comments, and the details about how to change them are listed in the file attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
I think the essence of the research is there. The experimental design, measurements, statistical analysis, and most of the essence seem adequate. The 'conclusions' tends to be more "Summary" and should be adjusted accordingly if the recommendations below are accepted.
However it is lost in translation. This article is almost completely incomprehensible in English. I think this submission was the first translation attempt, and should be withdrawn for major revision in consultation with a professional English as Second Language translator. I do not normally rewrite, but I will provide examples. Overall, I urge you to find professional translation assistance.
Notes first.
ammonium nitrate, NH4NO3, is usually 'scattered' as a dry material. You say "sprayed" which indicates it was dissolved. Is that what you wanted to say?
Tables should have the abbreviations used in the columns and lines defined within the table itself, in addition to being defined in the manuscript. This allows tables to be self-contained.
"nitrogen gradients" should be "nitrogen rates" throughout.
"season variation" should be "seasonal variation throughout.
the number of significant digits in the tables makes them very difficult to read.
"significantly manipulated" is a very unusual construct in the English language.
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Rewriting Examples:
Your version at the beginning of the abstract:
"The capability of forest ecosystem to sequester carbon from the atmosphere largely depends on the interaction of soil organic matter and nitrogen content and would be greatly influenced by the nitrogen deposition under the future scenario of the global change. It would help clarify this interaction to explore the variations of soil carbon fraction and soil respiration with the nitrogen deposition."
What I think you are trying to say:
Forest ecosystem capacity to sequester atmospheric carbon (C) depends on nitrogen (N) and soil organic matter (SOM) dynamics. This interaction could be altered by changing N deposition patterns in a changing climate, thus the effect of variations in N deposition on the interaction of SOM and corresponding soil respiration needs better characterization.
An excerpt from Conclusions:
"The input of the nitrogen in the form of nitrate significantly manipulated the inherent turnover of soil organic matter. The annual soil respiration and the fine root biomass were both decreased by the inorganic nitrogen addition. Similar effect of nitrogen addition was also found on the soil microbial carbon and the dissolved organic carbon content. However, nitrogen addition markedly enhanced the proportion of the cold season carbon emission in the annually cumulative soil respiration. The fine root biomass had the significantly correlation with the annual soil respiration, the MBC content and the SDOC content, and was presumed to play a core role in unentangling the interaction of nitrogen deposition and soil organic matter turnover."
What I think you are trying to say: (and this is primarily a summary, not conclusions either).
Nitrate form N significantly altered SOM turnover. Annual soil respiration and fine root biomass both decreased with inorganic N addition. Soil microbial C and dissolved C content also were decreased with N addition. Conversely, the cold season C emission proportion of annual soil respiration increased. Fine root biomass was significantly correlated with annual soil respiration, MBC, and SDOC, and thus indicated the interactions between N deposition and SOM turnover.
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I reiterate, you have the first draft. I don't expect you to use my examples, but I think they illustrate the clarity in English you need.
Good writing is rewriting! I first drafted this four days ago and 'significantly' changed today.
Author Response
Dear reviewer:
We are very grateful to you for reviewing and modifying our manuscript. You are also greatly appreciated for help editing the language of our paper. Your constructive comments largely increase the paper quality. Each error was revised strictly according to your comments. Specifically, the language of our paper was completely improved by the MDPI, the English editing services. A point-to-point response letter was attached in the file attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
After reviewing revisions and the response to reviewers, authors have addressed all my comments.
Author Response
Dear reviewer:
We are very grateful to you for your constructive comments on our manuscript and your recognition of our research.We further revised the deficiencies in our manuscript.
Thank very much
The best wishes to you.
Reviewer 2 Report
The authors have revised the manuscript based on the comments, which very much improved the manuscript. They also conducted an English language editing. However, there are still a lot of spelling mistakes, comma mistakes, etc. which make the reading really unpleasant, especially in the light that this is already a revised version.
The discussion has been improved, but could still be improved by not only comparing numbers with other literature (e.g. 273, 292-296), but trying to interpret results in the light of the hypotheses stated in the introduction. Furthermore, I feel that in the discussion in many cases causality between factors is discussed, but only correlations/associations were examined (e.g.,335, 347-348, 353 -357)
Specific comments:
Title: Pinus tabuliformis(lower case)
Abstract:
I my opinion, you should avoid abbreviations (RA, MBC, SDOC, etc) in the abstract
L16: abbreviation for N addition levels not necessary in abstract, for N0 you can write “control plot”
L22: Fine root biomass significantly decreased by an average of 43.55% in nitrogen treatment plots compared to the control plot.
Introduction:
L34-37: Since CO2 concentration is not the topic of the paper and is never mentioned again I would omit this sentence.
L40: How high is the annual rate to sustain function of terrestrial ecosystems? I think this is depended on the ecosystem-function you are looking at.
L54: determine, … influence…
L63: how did you test the interaction of fine root production and soil carbon fraction?
L70: temperate; what is meant by widely, can you give a percentage?
L76: were applied to twenty plots ... (delete ‘of soil’)
Material and Methods:
L90-93: write only species names in italics. Are all species necessary to mention? I would constrain to the most important ones.
L94: what do you mean by “middle slope”
L98: Shanxi province
L99: what do the numbers mean
L99: four levels, but you give five levels then: 0,5,10,20,40
L100: kg instead of g
L101: replace ‘was’ by ‘is’
L104: to ‘avoid’ cross-contamination?
L105: plants
L106: the maximum diameter at breast height (DBH) of the trees within the 20 forest plots was 36.2 cm.
L111: what are the four directions? (do you mean geographic directions?)
L113: did you measure soil temperature continuously over the observation period?
L114-117: Swap the two sentences.
L124: space between CO2 and m-2
L128: the experimental design
L139: delete ‘5’
Table 2: Rsi is missing.
Results
L177: The estimated Ra averaged…: averaged across all plots or N addition plots?
L185: its average contribution to RA
L186: why do you use N20 as reference and not N40 as before?
Table 4: You should add the abbreviation of the soil respiration estimate you have tested (Rsi)
L219: Do you mean: The production and nitrogen content of litter vs fine roots were ... (also in the subtitle)
L233: RA was correlated, ‘ascribe’ implies a causality which you can’t prove with your analysis
L242: the Figure5 shows the relationship the other way around
Discussion:
L247: what do you mean different temporal scales?
L252: add comma after ‘contrast’
L257: from a previous experiment…
L273: Do you have any explanation for this difference?
L278: add comma between ‘study’ and ‘which’
L281: content of
L297: were significantly decreased ‘in N addition plots’
L309-311: I do not understand this argumentation
L335: you have no evidence of a determination, you have just a correlation of SOC storage and soil nutrient content with soil respiration, same in L347-348, and 353 -357. From a correlation you can’t draw a causality and you should revise your statemetns accordingly
In all Tables: no point between Table and Nr: ‘Table 3’ instead of ‘Table.3’
Author Response
Dear reviewer
Thank you sincerely for your review on our manuscript. Your careful review has greatly increased the paper quality in article organization and result analysis. We have improved the details and corrected spelling mistakes under your comments and suggestions
Author Response File: Author Response.docx
Reviewer 3 Report
The revision is much clearer! Thank you for the response.
I have attached a marked copy with my queries and suggestions. Most of my suggestions hopefully go toward a more 'active' tense in your writing. I don't always give a suggestion though - Page 2, lines 62-64 needs rewording. The "much effort should still be paid . . ." passage has a passive tone that needs revision.
In some places, but not all, I have noted extraneous "-" marks that apparently carried over from prior versions.
Also on Page 2, lines 89 - 93 need attention to detail as to what should not be in italics.
On page 4, lines 130-32: it seems the sample consisted of a single augering. Is this correct?
I need to clarify my query on Page 10, lines 302-3. I mention lowering of pH by ammonium nitrate - normally that material does not acidify soil to the extent of other N fertilizers. What I am noting is that you have described an acid soil response (toxic Al, changing Mg and Ca availability). Are you ascribing this to your AN amendment or to atmospherically deposited N?
Another item on Page 10, at lines 319-22, it seems as if you are describing an active decision by the forest to assimilate N because the plants know that this is a change and they need to take advantage of it. I 'm not sure if you can give the plants a motive - they take it up because its there and they can.
You will see that I waded into the effect/affect controversy. I suggest you leave the final decision to the professional editors - as that is what I would do!
A strength of your work is the attention to detail: both in the execution of the study, and doing your homework. I appreciate your detailed exploration of the global literature that is relevant to both doing your project, and to interpreting it.
I am glad to have had this opportunity and wish you the best going forward.
Comments for author File: 
Comments.pdf
Author Response
Dear reviewer
Thank you sincerely for your review on our manuscript. Your careful review and valuable suggestions have greatly increased the paper quality. We have improved the details and corrected spelling mistakes under your comments and suggestions. The details about how to change them are listed in the file attachment.
Thank you very much
Best wishes to you！
Author Response File: Author Response.docx
